1. Field of the Invention
This invention relates to a separating mechanism for forcibly separating transfer medium from an image bearing member after the visible image on the image bearing member has been transferred to the transfer medium.
2. Description of the Prior Art
Generally, in the image formation apparatus utilizing electrophotography such as an electrophotographic copying apparatus, a photosensitive medium having a photoconductive layer shaped in the form of a drum, for example, is used as the electrostatic latent image bearing member to form a copy image of an original thereon as the photosensitive medium is rotated. In such an apparatus, charging means, exposure means and developing means are disposed around the rotating photosensitive medium to form an electrostatic latent image corresponding to the original image and the latent image is developed by toner particles. The visible image obtained by the development on the photosensitive medium is then transferred to transfer medium such as plain paper or the like and fixed on such transfer medium for utilization. On the other hand, after the image transfer has been effected, the photosensitive medium is cleaned by cleaning means to remove any residual developer therefrom for reuse in the next cycle of copy image formation.
To transfer the developer to the transfer medium during the image transfer, it is necessary to have an effect on the electric field by the use of voltage application means such as corona discharger, roller electrode or the like. Corona discharger is widely used as such voltage application means, but when charge is so imparted to the transfer medium, the charge and the latent image on the photosensitive medium attract each other intensely, so that the transfer medium is brought into strong intimate contact with the photosensitive medium. Such intimate contact is necessary for the toner particles to be transferred to the transfer medium without being disturbed during the image transfer step. However, after completion of the image transfer step, the transfer medium must be forcibly separated from the photosensitive medium by some separation means in order to direct the transfer medium to the fixing means. Heretofore, vacuum suction system, a compressed air blower system whereby pressurized air may be blown through a nozzle, or other blower means have been employed as the means for separating the transfer medium brought into strong intimate contact with the photosensitive medium. The separating mechanism using the compressed air requires a compressor, pump or other machine and a conduit for directing the compressed air to a set position. As a result, various problems occur such as bulkiness of the image formation apparatus, higher cost of manufacture and even the generation of noise.
A solution to the problems occuring to the separating mechanism using compressed air is a separating system utilizing a separation belt as shown in FIG. 1 of the accompanying drawings. FIG. 1 shows a side view of an example of the separating mechanism using a belt. In the Figure, reference numeral 1 designates a drum-shaped photosensitive medium (hereinafter referred to as the photosensitive drum) which is rotatable in the direction of the arrow. Designated by 2 is a separation guide which is a metal plate provided at a position whereat the end of the transfer paper 3 overlaps the end of the photosensitive drum. The base of the separation guide 2 forms a fixed end 2a fixed as shown and the other end is a free end 2b which is spaced apart from the peripheral surface of the drum. Denoted by 4 is a separation roller formed by a rotatable roller extending parallel to the rotational axis of the photosensitive drum. At the location of the separation roller 4 corresponding to the separation guide 2, an endless belt 8 passed over pulleys 5, 6 and 7 is urged against the roller 4 as shown. The separation roller 4 and the separation belt 8 are rotated in the direction of the arrows to guide and separate the transfer medium in the direction of arrow 10.
According to the above-described separation mechanism, it is possible to separate the transfer medium from the photosensitive drum by a simple construction. In such construction, however, when abnormal transport of transfer medium occurs at the image transfer position or the separating position, great difficulties are encountered in treating the transfer medium because the separation guide 2 is fixed. Also, the mounting or dismounting of the drum 1 with respect to the apparatus body could not be effected quickly because the separation guide 2 is urged against or fixed adjacent to the drum 1.